1. Field of the Invention
The present invention relates to a technology for processing alarms in a transmission apparatus such as an ADM apparatus with a path switch ring function by means of a path switch, and a bi-directional line switch ring function by means of a service selector, etc.
2. Description of the Related Art
These days, with the advent of large-scale and urbanized networks composing optical transmission systems, the implementation of an add drop multiplexer (ADM) apparatus is required in order to construct a ring type network which can cope with large-scale networks and the urbanization of networks.
When the ring type network implemented by an ADM apparatus is classified by a transmission form and a form of failure prevention, a path switch ring (uni-directional path switch ring)(hereinafter called PSR) and a bi-directional line switch ring (BLSR) are publicly known. However, both rings are required to be implemented by means of one ADM apparatus so that customers may construct an optimal network.
FIG. 1 shows the configuration of both an ADM apparatus and a general-purpose optical transmission network constructed using an ADM apparatus.
To implement this network ITU-T established an SDH transmission system, and in North America a transmission interface based on this transmission system and called a synchronous optical network (SONET) is used.
In the SONET interface a signal OC-N (or STS-N) is used which is based on a signal with a transmission rate of 51.84 Mbit/second called a synchronous transport signal-level 1(STS-1) or an optical carrier-level 1(OC-1), and has a transmission rate N (integer) times as fast as the STS-1 or OC-1 signal. In the example shown in FIG. 1, OC-3 (or STS-3), OC-12 (or STS-12) and OC-48 (or STS-48) with transmission rates 3, 12 and 48 times as fast as the STS-1 (OC-1) signal, respectively, are shown.
FIG. 2 shows the frame format of an STS-1 signal. The STS-N (OC-N) signal has a structure in which N pieces of STS-1 (OC-1) signals shown in FIG. 2 are multiplexed by way of byte multiplication.
As shown in FIG. 2, the STS-1 frame is divided into two areas, one area is called a transport overhead for transmitting overhead information, and the other area is called a synchronous payload envelope for transmitting payload information. Besides the information payload being user information, the synchronous payload envelope transmits overhead information called a path overhead. The transport overhead comprises an area called a section overhead and an area called a line overhead. The overhead area is used to transmit various kinds of control information and alarms between transmission apparatuses (ADM apparatus, etc.) composing a network.
The STS-1 frame shown in FIG. 2 is transmitted byte by byte in order from the top line to the bottom line, and from the left to the right.
In the information payload, digital signals of a plurality of users are multiplexed.
On the other hand, section, line and path overhead areas for classifying the overhead are concepts for identifying communication spans composing the SONET network.
The path specifies end-to-end connection between a transmission apparatus for generating one STS-1 frame and a transmission apparatus for terminating the frame, and the path overhead transmits overhead information communicated between both above-mentioned transmission apparatuses using the end-to-end connection. Although one STS-1 frame is transmitted via various kinds of physical media (OC-1, OC-3, OC-12 and OC-48) on the way, a path corresponding to the STS-1 signal is specified independently of those media.
The line specifies connection in which physical characteristics are continuous, more specifically connection between optical fiber spans with the same transmission rate, and the line overhead transmits overhead information communicated between transmission apparatuses at both ends of the physically continuous connection.
The section specifies connection between network elements such as a lightwave regenerator inserted between the above-mentioned lines, and the section overhead transmits overhead information communicated between the network elements.
As described above, since in the STS-1 frame, overhead information is layered and stored in an overhead area corresponding to both communication range and communication characteristics, and transmitted, and thereby, since it is sufficient for each network apparatus to process only overhead information related to itself, an efficient communication control can be implemented.
FIG. 3 shows the structure of the section overhead and line overhead in the transport overhead, and each overhead byte of a path overhead in a synchronous payload envelope. Out of these, overhead bytes particularly related to the present invention are described later.
Returning to the explanation of FIG. 1, ADM apparatuses 101 are apparatuses with a function to mutually connect optical fibers for ADD/DROP-transmitting OC (STS) signals with different transmission rates. The ADM apparatus 101 shown in FIG. 1, for example, connects an optical fiber for transmitting an OC-48 signal with an optical fiber for transmitting an OC-12 signal.
To implement the above-mentioned signal switching function, the ADM apparatus 101 comprises a time slot assigning (TSA) unit 102 and a multiplexer unit (THRU/ADD unit) 103.
The TSA unit 102 has a function to multiplex an arbitrary STS-1 frame multiplexed in the OC (STS) signal of the input side, to a signal with an arbitrary STS-1 frame timing in the OC signal of the output side, and has a configuration, for example, as shown in FIG. 4.
FIG. 4 shows the case where an input side main signal is an OC-48 main signal consisting of 48 channels, and where an output side main signal is an OC-N signal consisting of N channels.
Channels 1 to 48 (each channel corresponds to one STS-1 signal) of the input side main signal are inputted to N switches 401 #1 to #N. Each switch 401 is designated which channel to select and to output by a TSA control signal, and sends the channel at the STS-1 frame timing of the output side main signal to which the switch 401 is assigned.
In FIG. 1 the TSA unit 102 (DROP) multiplexes (drops) an arbitrary STS-1 frame multiplexed in the OC-48 signal being a higher order group side, to a signal with an arbitrary STS-1 frame timing in the OC-12 signal being a lower order group side.
On the other hand, the TSA unit 102 (ADD) multiplexes (adds) an arbitrary STS-1 frame multiplexed in the OC-12 signal being a lower order group side, to a signal with an arbitrary STS-1 frame timing in the OC-48 signal being a higher order group side, and an ADD signal obtained as this result is mixed with the OC-48 signal by the THRU/ADD unit 103.
Next, the PSR is described below.
FIG. 5 shows the configuration of the PSR.
An ADM apparatus 501 used in a PSR configuration comprises TSA units 502 (E-ADD) and 502 (W-ADD) and THRU/ADD (T/A) units 503 (E) and 503 (W) for multiplexing (adding) an ADM signal 505 from a lower order group side optical fiber, to a higher order group optical fiber, TSA units 502 (E-DROP) and 502 (W-DROP) for multiplexing (dropping) a DROP signal 506 from a higher order group side optical fiber, to a lower order group side optical fiber, and a path switch (PSW) 504.
Then, in an ADM apparatus 501(#1) an ADD signal 505 (#1) from a lower order group side optical fiber is added to an outer optical fiber 507(OUTER) by the operation of both TSA unit 502(E-ADD) and THRU/ADD unit 503(E), and is added to an inner optical fiber 507(INNER) by the operation of both TSA unit 502(W-ADD) and THRU/ADD unit 503 (W). In this way, over both optical fiber 507(OUTER) and optical fiber 507(INNER) the same optical signal is transmitted.
The optical signal added from the ADM apparatus 501#1 and redundantly transmitted on dual rings, for example, is dropped at the ADM apparatus 501#2.
That is, in the ADM apparatus 501#2, an optical signal from the optical fiber 507(OUTER) is dropped by the TSA unit 502(W-DROP), and an optical signal from the optical fiber 507(INNER) is dropped by the TSA unit 502(E-DROP). Basically both TSA unit 502(W-DROP) and TSA unit 502(E-DROP) drop the same signal.
As shown in FIG. 6, the ADM apparatus 501 comprises an alarm detecting unit 601 (W-DROP) for detecting alarms in the overhead area (see FIGS. 2 and 3) of one or more STS-1 frames provided in the signal dropped by the TSA unit 502(W-DROP), an alarm detecting unit 601(E-DROP) for detecting alarms from each of the overhead areas of one or more STS-1 frames provided in the signal dropped by the TSA unit 502(E-DROP), and a comparing unit 602 for comparing an alarm detected on the W-DROP side with an alarm detected on the E-DROP side for each STS-1 frame timing.
That is, the TSA unit 502 has a configuration as shown in FIG. 4. As shown in FIG. 7, signals are cross-connected in a form where a main signal and an overhead area containing alarm information are mixed, and the alarm detecting unit 601 detects alarms by separating both the main signal and the overhead area containing alarm information from the output.
Then in FIGS. 5 and 6, a path switch (PSW) 504 selects an output in which alarms are not detected by the comparing unit 602 (DROP) (if alarms are not detected in both outputs, a default signal is output) out of the outputs of both TSA unit 502 (W-DROP) and TSA unit 502 (E-DROP) for each STS-1 frame timing in the lower order group side signal, and outputs the output to the lower order group side optical fiber as a DROP signal 506.
In this way, the ADM apparatus 501#2 can select a signal in which abnormalities are not detected, that is, a normal signal out of both the STS-1 signal transmitted on the outer optical fiber 507 (OUTER) and the STS-1 signal transmitted on the inner optical fiber 507(INNER), and drop the signal to the lower order group side optical fiber. That is, the ADM apparatus 501 with a PSR configuration is characterized in that a network configuration in which dual rings in one network can be selected in units of STS-1 frames as a running path and a stand-by path,can be implemented.
On the contrary, for an optical signal transmitted from the lower order group side optical fiber connected to the ADM apparatus 501#2, to the lower order group side optical fiber connected to the ADM apparatus 501#1, ADD/DROP processing for each of the optical fibers 507(OUTER) and 507(INNER) composing the PSR can be implemented by each of the above-mentioned ADM apparatuses 501#1 and 501#2 executing an operation the reverse of the above-mentioned operation.
It must be noted that as shown in FIG. 6, in order to control the PSW 504, it is necessary for the ADM apparatus 501 with the above-mentioned PSR function to comprise two alarm detecting units 601(W-DROP) and 601(E-DROP) for detecting alarms from the outputs of the TSA units 502(W-DROP) and 502(E-DROP), respectively.
Nest, the BLSR is described below.
FIG. 8 shows the bridge configuration of a plurality of rings in which an ADM apparatus 801 which has a BLSR configuration is used, and FIGS. 9 and 10 explain the failure restoration carried out by the rings.
The ADM apparatus with a BLSR configuration can easily connect two ring networks redundantly.
That is, it is assumed here that when two networks RING1 and RING2 are connected with each other by both PRIMARY ADM apparatus 801 composing RING1 and PRIMARY ADM apparatus 801 composing RING2, a failure, etc. occurs in either of the STS-1 frames of the OC (STS) signal transmitted on the connecting line.
In this case, as shown in FIG. 11, the respective PRIMARY ADM apparatuses 801 in RING1 and RING2 cut the connection between both PRIMARY ADM apparatuses 801 only for STS-1 frame timings in which there is a failure, etc., by controlling a unit called a service selector (SS) 803, and put an optical fibers 802(OUTER) and 802(INNER) in a through state. As for STS-1 frame timings in which there is no failure, etc., the current connection is maintained.
Simultaneously, as shown in FIG. 10, the respective SECONDARY ADM apparatuses 801 in RING1 and RING2 modify the through control for both optical fibers 802(OUTER) and 802(INNER) in each ring only for STS-1 frame timings in which there is the above-mentioned failure, by controlling the SS 803, and establishes connection between both SECONDARY ADM apparatuses 801.
In this way, the ADM apparatus with a BLSR configuration 801 can switch over a work line to a protection line, and vice versa in units of STS-1 frames between two networks.
The detailed operation of the ADM apparatus for implementing the above-mentioned function is described below referring to FIGS. 8 and 11.
First, the operation in the case where connection is established between the respective PRIMARY ADM apparatuses 801 of RING1 and RING2, is described.
In the PRIMARY ADM apparatus 801 of RING1, a selector (E/W SEL) 804 selects an optical signal dropped from the inner optical fiber 802(INNER) of RING1 by the TSA unit 502(E-DROP) out of both optical signals dropped from the inner optical fiber 802(INNER) of RING1 by the TSA unit 502(E-DROP) and the optical signal dropped from the outer optical fiber 802(OUTER) of RING1 by the TSA unit 502(W-DROP), and outputs the optical signal to the RING2 side.
On the other hand, in the SECONDARY ADM apparatus 801 of RING2, an SS 803(W) selects an optical signal from RING1 added by the TSA unit 502(W-ADD) out of both the optical signal from RING1 added by the TSA unit 502(W-ADD) and optical signal input from the inner optical fiber 802(INNER) of RING2, and outputs the optical signal to the optical fiber 802(INNER) of RING2.
On the contrary, in the PRIMARY ADM apparatus 801 of RING2, a selector (E/W SEL) 804 selects an optical signal dropped from the outer optical fiber 802(OUTER) of RING2 by the TSA unit 502(W-DROP) out of both the optical signal dropped from the outer optical fiber 802(OUTER) of RING2 by the TSA unit 502(W-DROP) and the optical signal dropped from the inner optical fiber 802(INNER) of RING2 by the TSA unit 502(E-DROP), and outputs the optical signal to the RING1 side.
On the other hand, in the PRIMARY ADM apparatus 801 of RING1, an SS 803(E) selects an optical signal from RING2 added by the TSA unit 502(E-ADD) out of both the optical signal from RING2 added by the TSA unit 502(E-ADD) and the optical signal input from the outer optical fiber 802(OUTER) of RING1, and outputs the optical signal to the optical fiber 802(OUTER) of RING1.
In the PRIMARY ADM apparatus 801 of RING1, an SS 803(E) selects an optical signal from RING2 added by the TSA unit 502(E-ADD) out of both the optical signal from RING2 added by the TSA unit 502(E-ADD) and the optical signal input from the optical fiber 802(OUTER) of RING1, and outputs the optical signal to the optical fiber 802(OUTER) of RING1.
In the PRIMARY ADM apparatus 801 of RING1, an SS 803(W) selects an optical signal input from the optical fiber 802(INNER) of RING1 out of both the optical signal from RING2 added by the TSA unit 502(W-ADD) and the optical signal input from the optical fiber 802(INNER) of RING1, and puts each STS-1 frame in the optical fiber 802(INNER) of RING1 in a through state.
In the same way, in the PRIMARY ADM apparatus 801 of RING2, an SS 803(E) selects an optical signal input from the optical fiber 802(OUTER) of RING2 out of both the optical signal from RING1 added by the TSA unit 502(E-ADD) and the optical signal input from the optical fiber 802(OUTER) of RING2, and puts each STS-1 frame in the optical fiber 802(OUTER) of RING2 in a through state.
In this way, connection as shown in FIG. 9 is established between the PRIMARY ADM apparatuses 801 of RING1 and RING2.
The operation in this case of the respective SECONDARY ADM apparatuses 801 of RING1 and RING2 is described below.
In the SECONDARY ADM apparatus 801 of RING1 a selector (E/W SEL) 804 selects an optical signal dropped from the inner optical fiber 802(INNER) of RING1 by the TSA unit 502(E-DROP) out of both the optical signal dropped from the inner optical fiber 802(INNER) of RING1 by the TSA unit 502(E-DROP) and the optical signal dropped from the outer optical fiber 802(OUTER) of RING1 by the TSA unit 502(W-DROP), and outputs the optical signal to the RING2 side.
On the other hand, in the PRIMARY ADM apparatus 801 of RING2, an SS 803(W) selects an optical signal input from the inner optical fiber 802(INNER) of RING2 out of both the optical signal from RING1 added by the TSA unit 502(W-ADD) and the optical signal input from the inner optical fiber 802(INNER) of RING2, and puts each STS-1 frame in the optical fiber 802(INNER) of RING2 in a through state.
On the contrary, in the SECONDARY ADM apparatus 801 of RING2, a selector (E/W SEL) 804 selects an optical signal dropped from the outer optical fiber 802(OUTER) of RING2 by the TSA unit 502(W-DROP) out of both the optical signal dropped from the outer optical fiber 802(OUTER) of RING2 by the TSA unit 502(W-DROP) and the optical signal dropped from the inner optical fiber 802(INNER) of RING2 by the TSA unit 502(E-DROP), and outputs the optical signal to the RING1 side.
On the other hand, in the SECONDARY ADM apparatus 801 of RING1, an SS 803(E) selects an optical fiber input from the outer optical fiber 802(OUTER) of RING1 out of both the optical fiber from RING2 added by the TSA unit 502(E-ADD) and the optical fiber input from the outer optical fiber 802(OUTER) of RING1, and puts each STS-1 frame in the optical fiber 802(OUTER) of RING1 in a through state.
In this way, a through connection shown in FIG. 9 is established in the respective SECONDARY ADM apparatuses 801 of RING1 and RING2.
It is assumed that in the above-mentioned connecting state shown in FIG. 9 there is a failure, etc. in either of the STS-1 frames of the OC(STS) signal transmitted on the connection line between the PRIMARY ADM apparatuses 801 of RING1 and RING2.
In this case, the connection controlling state shown in FIG. 10 is implemented for the STS-1 frame timing in which there is a failure, etc. by carrying out control the exact reverse of the above-mentioned control, in the respective PRIMARY ADM apparatuses 801 and the respective SECONDARY ADM apparatuses 801 of RING1 and RING2.
The ADM apparatus with a BLSR configuration 801 is provided with an alarm detecting mechanism as shown in FIG. 11, so that the ADM apparatus with a BLSR configuration 801 may implement the above-mentioned control for the avoidance of failure.
First, the ADM apparatus 801 comprises an alarm detecting unit 1101 (E-ADD) for detecting alarms from the overhead area (see FIGS. 2 and 3) of one or more STS-1 frames multiplexed in an OC(STS) signal cross-connected with an ADD signal 1103 by the TSA unit 502(E-ADD) and added to an optical fiber 1105(OUTER) by the TSA unit 502(W-DROP), an alarm detecting unit 1101(W-THRU) for detecting alarms from the overhead area of one or more STS-1 frames multiplexed in an OC(STS) signal input the optical fiber 1105(OUTER), and a comparing unit 1102(E) for comparing an alarm detected in the E-ADD side with an alarm detected on the W-THRU side for each STS-1 frame timing.
The SS 803(E) selects an output in which alarms are not detected by the comparing unit 1102 (E) (if alarms are not detected in both outputs, a default is output) out of both the output of the TSA unit 502 (E-ADD) and the input from the optical fiber 1105(OUTER) for each STS-1 frame timing, and outputs the output to the optical fiber 1105(OUTER).
In the same way, the ADM apparatus 801 comprises an alarm detecting unit 1101 (W-ADD) for detecting alarms from the overhead area of one or more STS-1 frames multiplexed in an OC(STS) signal cross-connected with an ADD signal 1103 and added to an optical fiber 1105(INNER) by the TSA unit 502(W-ADD), an alarm detecting unit 1101(E-THRU) for detecting alarms from the overhead area of one or more STS-1 frames multiplexed in an OC(STS) signal input from the optical fiber 1105(INNER), and a comparing unit 1102(W) for comparing an alarm detected in the W-ADD side with an alarm detected on the E-THRU side for each STS-1 frame timing.
The SS 803(W) selects an output in which alarms are not detected by the comparing unit 1102 (W) (if alarms are not detected in both outputs, a default is output) out of both the output of the TSA unit 502 (W-ADD) and the input from the optical fiber 1105(INNER) for each STS-1 frame timing, and outputs the output to the optical fiber 1105(INNER).
In this way, the connection between the PRIMARY ADM apparatuses 801 of RING1 and RING2 and the connection between the SECONDARY ADM apparatuses 801 of RING1 and RING2 can be switched over between each other in units of STS-1 frames. That is, the ADM apparatus 801 with a BLSR function is characterized in a network configuration in which both work line and protection line can be secured in units of STS-1 frames between two networks.
It must be noted that, as shown in FIG. 11, it is necessary for the ADM apparatus 801 with the above-mentioned BLSR function to comprise four alarm detecting units 1101(E-ADD), 1101(W-ADD), 1101(W-THRU) and 1101(E-THRU) for detecting each alarm in the respective outputs from the TSA units 502(E-ADD) and 502(W-ADD) and the respective input from the optical fibers 1105(OUTER) and 1105(INNER).
Although, as described above, conventionally two kinds of ADM apparatus, an ADM apparatus with a PSR function and an ADM apparatus with a BLSR function, are publicly known, it is required that both rings can be implemented by means of one ADM apparatus so that customers may construct an optimal network in accordance with their purposes.
From this point of view, the incorporation of the configuration of an ADM apparatus with the PSR function 501 shown in FIG. 6 and the configuration of an ADM apparatus with the BLSR function 801 shown in FIG. 11 is considered. FIG. 12 shows the configuration of a conventional ADM apparatus with both the PSR function and BLSR function.
Since the respective configuration of four TSA units 502(E-ADD), 502(W-ADD), 502(E-DROP) and 502(W-DROP) in both FIGS. 6 and 11 is the same, the four TSA units 502 can be commonly used for both the PSR function and BLSR function as shown in FIG. 12.
The applied positions of both THRU/ADD unit 503(E) shown in FIG. 6 and SS 803(E) shown in FIG. 11 are the same. For this reason, as shown in FIG. 12, both units can be commonly used for both PSR function and BLSR function. The same applies to both THRU/ADD unit 503(W) shown in FIG. 6 and SS 803(W) shown in FIG. 11.
The applied positions of both PSW 504 shown in FIG. 6 and E/W SEL 804 shown in FIG. 11 are the same. For this reason, as shown in FIG. 12, by implementing one unit with the function of both units, the unit can be commonly used for both the PSR function and BLSR function.
Next, the alarm detecting unit is described.
In order to control a PSW 504 for implementing the PSR function as an alarm detecting unit, two alarm detecting units 601(W-DROP) and 601(E-DROP) for detecting each alarm in the respective output of TSA units 502(W-DROP) and 502(E-DROP), and one comparing unit 602(DROP) are needed. Since these alarm detecting units 601 have to detect an alarm from the overhead area of one or more STS-1 frames multiplexed in an OC(STS) signal after dropping, the alarm detecting units 601 have to be provided on the respective output side of TSA units 502(W-DROP) and 502(E-DROP).
On the other hand, in order to control two SS 803s for implementing the BLSR function, four alarm detecting units 1101(E-ADD), 1101(W-ADD), 1101(W-THRU) and 1101(E-THRU) for detecting each alarm from the respective outputs of TSA units 502(E-ADD) and 502(W-ADD) and optical fibers 1105(OUTER) and 1105(INNER), and two comparing units 1102(E) and 1102(W) are needed. Since out of these units two alarm detection units 1101(E-ADD) and 1101(W-ADD) have to detect an alarm from the respective overhead area of one or more STS-1 frames multiplexed in an OC(STS) signal after adding, the alarm detecting units 1101 have to be provided on the respective output sides of TSA units 502(E-ADD) and 502(W-ADD). Since two alarm detecting units 1101(W-THRU) and 1101(E-THRU) have to detect an alarm from the respective overhead area of one or more STS-1 frames multiplexed in an OC(STS) signal in the optical fibers 1105, the two alarm detecting units 1101 have to be provided on the respective input sides of those optical fibers 1105.
In this way, it is understood that in a conventional ADM apparatus with both PSR function and BLSR function, six alarm detecting units in total are required.
However, since the alarm detecting unit has to detect a predetermined byte value from each area of the section overhead, line overhead and path overhead of the frame for each STS-1 frame with the structure shown in FIG. 2 in a target OC(STS) signal, and has to execute judging and calculating processes, the circuitry scale of the alarm detecting unit becomes large.
Therefore, as shown in FIG. 12, the system has a problem that the provision of six alarm detecting units leads to a large-scale ADM apparatus, which causes an increase in the cost of the ADM apparatus.
The present invention has been made from the above-mentioned background, and it is an object of the present invention to reduce the scale of hardware needed to detect alarms.
One mode of the present invention presumes a transmission apparatus comprising a first main signal frame switching unit (TSA unit 502(E-DROP)) for executing a first frame switching process for each of all or a part of frames (STS-1 frame) in a first transmission signal on a first line (optical fiber 106(INNER) to which one or more frames including an area for displaying alarms, are multiplexed, a second main signal frame switching unit (TSA unit 502(W-DROP)) for executing a second frame switching process for each of all or a part of frames (STS-1 frame) in a second transmission signal on a second line (optical fiber 106(OUTER) to which one or more frames including an area for displaying alarms, are multiplexed, a switching unit (PSW 1302) for selecting either output of the first and second main signal frame switching processes and outputting the output to a third line, a third and fourth main signal frame switching unit (TSA units 502(W-ADD) and 502(E-ADD)) for executing third and fourth frame switching processes for each of all or a part of frames in a fourth transmission signal on a fourth line to which one or more frames including an area for displaying alarms, are multiplexed, a first service selector unit (SS 1301(W)) for selecting either output of the third main signal frame switching unit or input of a first line in units of frames and outputting the output or input to the first line, and a second service selector unit (SS 1301(E)) for selecting either the output of the fourth main signal frame switching unit or the input of a second line in units of frames and outputting the output or input to the second line. Generally speaking, a transmission apparatus like this is implemented as an ADM apparatus with both the path switching function and bi-directional line switching function.
In the present invention, a first alarm detecting unit (alarm detecting unit 1101(E-THRU)) detects each alarm corresponding to each frame contained in a first transmission signal, from the input side of the first transmission signal.
A second alarm detecting unit (alarm detecting unit 1101 (W-THRU)) detects each alarm corresponding to each frame contained in a second transmission signal, from the input side of the second transmission signal.
First and second alarm switching unit (alarm TSA apparatuses 1303 (E-DROP) and 1303 (W-DROP)) execute the switching processes in the same frame order as the first and second main signal frame switching processes, respectively for an alarm of the respective frame output by the first and second alarm detecting unit.
A first comparing unit (comparing unit 602 (DROP)) makes the switching unit select either of the outputs of the first and second main signal frame switching processes, in units of frames, by comparing alarms of the respective frame output by the first and second alarm switching unit with each other.
A third alarm detecting unit (alarm detecting unit 107 (ADD)) detects each alarm corresponding to each frame contained in a fourth transmission signal, from the fourth transmission signal.
Third and fourth alarm switching unit (alarm TSA apparatuses 1303 (W-ADD) and 1303 (E-ADD)) execute the switching process in the same frame order as the third and fourth main signal frame switching processes, respectively for an alarm for each frame outputted by the third alarm detecting unit.
Second and third comparing unit (comparing units 1102 (W) and 1102 (E)) control the first and second service selector unit by comparing an alarm for each frame output by the third and fourth alarm switching unit with an alarm for each frame detected by the first and second alarm detecting unit.
By adopting the above-mentioned configuration of the present invention, in a transmission apparatus such as an ADM apparatus with both the path switch ring function and bi-directional line switch ring function, the number of alarm detecting unit with large-scale circuitry can be reduced, and the scale of hardware can also be greatly reduced compared with the prior art.
The present invention can be so constructed that an OR operation may be executed by both the alarm for each frame output by the first and second alarm switching unit or the third and fourth alarm switching unit, and the signal indicating that a line is set to xe2x80x9cunconnectedxe2x80x9d for each frame, and that the result of the operation may be input to the first comparing unit, or the second and third comparing unit.
By adopting this configuration, a line unconnected state can be easily set for a transmission apparatus.
In the above-mentioned configuration of the present invention, the present invention can be so constructed as to further comprise an alarm reporting circuit for reporting the respective alarm for each frame outputted by the first and second alarm switching circuits or the respective alarm for each frame outputted by the third and fourth alarm switching circuits, and the respective alarm for each frame outputted by the first and second alarm detecting circuits, as alarm monitor information.
By adopting this configuration, the detected state of various kinds of alarms in a transmission apparatus can be monitored externally.
Furthermore, the above-mentioned invention can be so configured as to further comprise a coding unit for coding each alarm input to the first and second alarm switching unit or each alarm input to the third and fourth alarm switching unit, and a decoding unit for decoding each coded alarm output from the first and second alarm switching unit or each encoded alarm output from the third and fourth alarm switching unit.
By adopting this configuration, the bit number of each alarm detection result signal to be processed by an alarm switching unit can be further reduced, and the hardware scale of the transmission apparatus can be further reduced.